This is just a proof of concept, since most definitions should just be
notations for the realization to be user-friendly. Moreover, the format of
the file will presumably evolve, if only for some information to properly
update it when the theories change.
Remark about the theory : Lemma mul_assoc_div has an extraneous hypothesis.
Indeed, as long as inverse is a total function, this lemma is an immediate
consequence of multiplication associativity.

How to use it:
why3 --realize -D drivers/coq-realize.drv -T real.Real -o .
produces Real.v in the current directory
why3 --realize -D drivers/coq-realize.drv -T real.Real
produces real/Real.v in the loadpath near real.why
(the directory "real" must exist)
If a realization file is already there, it is passed to
the printer in order to preserve the proofs.
Instead of -D <driver_file>, you can use -P <prover>,
if that prover uses a corresponding driver. However,
the prover itself is not used.
You can only realize theories from the loadpath.
At the moment, coq-realize.drv is the only driver
capable to realize theories in some sensible way.
For any other driver, the results may be funny.
Realization of WhyML modules is not possible so far.
Realization may break if you directories and filenames
contain non-alphanumeric symbols.
The whole thing is in very preliminary stage.
Use with caution.

When the user wants to write a Coq proof, she needs to run Coq on the goal,
wait five seconds for it to fail (it will fail, otherwise there is no point
in running Coq on this goal: another prover would have succeeded already),
and finally edit it. This is a waste of time. So goals run with an
interactive prover are now marked as unknown until their file is edited.
Interactive provers could have been detected by a nonempty "editor" string,
but there are interactive provers that don't have dedicated editors, and
there might be automated provers with dedicated user interfaces. So a new
field was added to prover descriptions.
TODO: actually run the editor when there is only one selected goal,
rather than keeping the current three-click method of editing proofs.